Observations of Ly$$\alpha $$ Emitters at High Redshift

Abstract

In this series of lectures, I review our observational understanding of highz Lyα emitters (LAEs) and relevant scientific topics. Since the discovery of LAEs in the late 1990s, significant progresses in LAE studies have been made over the past two decades by deep multi-wavelength observations. More than ten (one) thousand(s) of LAEs have been identified photometrically (spectroscopically) in optical and near-infrared data, and the redshifts of these LAEs range from z ∼ 0 to z ∼ 10. These large samples of LAEs are useful to address two major astrophysical issues, galaxy formation and cosmic reionization. Statistical studies have revealed the general picture of LAEs' physical properties: young stellar populations, remarkable luminosity function evolutions, compact morphologies, highly ionized inter-stellar media (ISM) with low metal/dust contents, low masses of dark-matter halos. Typical LAEs represent low-mass high-z galaxies, high-z analogs of dwarf galaxies, some of which are thought to be candidates of population III galaxies. These observational studies have also pinpointed rare bright Lyα sources extended over ∼ 10 − 100 kpc, dubbed Lyα blobs, whose physical origins are under debate. LAEs are used as probes of cosmic reionization history through the Lyα damping wing absorption given by the neutral hydrogen of the inter-galactic medium (IGM), which complement the cosmic microwave background radiation and 21cm observations targeting the epoch of reionization. The low-mass and highly-ionized population of LAEs can be major sources of cosmic reionization, and physical parameters including the ionizing photon escape fraction have been extensively investigated. The budget of ionizing photons for cosmic reionization has been constrained, although there remain large observational uncertainties in the parameters. Beyond these two established topics of LAEs, galaxy formation and cosmic reionization, several new usages of LAEs for science frontiers have been suggested such as the distribution of HI gas in the circum-galactic medium and filaments of large-scale structures. Ongoing 10 mclass optical telescope programs and future telescope projects, such as JWST, ELTs,

A New Constraint on the Simulation of the Intergalactic Medium through the Evolution of the Neutral Hydrogen Fraction in the Epoch of Reionization

“…The observational data we compared to the simulations are listed in Table 3. The technique has been used in Fan et al (2006) and considers the Gunn-Peterson optical depth (τ = 0.066 ± 0.013) in (McGreer et al 2015;Banados et al 2018) is the "Dark Gaps in Quasars Spectra," in (Schenker et al 2014;Tilvi et al 2014;McGreer et al 2015) is the "prevalence of the Lyα emission in galaxies" (Schenker et al 2014;Bouwens et al 2015), in Davies et al (2018) is "Quasars Continuum," in Totani et al (2006), Lyα "Damping Wing of quasars and Gamma-ray burst," in Ouchi 2019) We analyzed both simulation and observational data and decided which simulated model describes the IGM better. The changes in neutral hydrogen in all models are displayed in Figure 1.…”

“…If their ionizing photons have a high enough escape percentage, early-forming galaxies can be powerful ionizing sources. The typical (or effective) value of f esc is not yet defined, although it is a major parameter for comprehending the cosmic reionization process (Ouchi 2019).…”

Broadband Intensity Mapping of the Ultraviolet-Optical Background with CASTOR and SPHEREx

“…The 30% constraint on the Lyα equivalent width provides a window into the population of Lyman α emitters (LAEs) at high redshift (Ouchi 2019 meter class telescopes and limit the population of identified LAEs up to z ≈ 8 to 10 3 − 10 4 (Konno et al 2016). In contrast, our technique measures the population statistics of Lyα emitters at z = 5−9 without identifying individual LAEs.…”

Revisiting the emission line source detection problem in integral field spectroscopic data

“…The continuous spatial and spectral coverage provided by wide‐field IFS avert the classical spectroscopic survey paradigm of target pre‐selection for follow‐up spectroscopy, as these observations provide literally “spectroscopy of everything” within the observed fields. This concept is also utilized in the Hobby Eberly Telescope Dark Energy Experiment (HETDEX; Gebhardt et al, 2021; Hill et al, 2021), a dedicated IFS survey facility for Lyman $$$ \alpha $$$ (Ly $$$ \alpha $$$ $$$ \lambda 1216 $$$) emitting galaxies (LAEs; Ouchi, 2019), that aims at constraining the Dark Energy equation of state. Given their pivotal importance in addressing fundamental astrophysical and cosmological questions the next generation of wide‐field IFS are already envisioned (e.g., as part of the ESO Spectroscopic Facility; Pasquini et al, 2018) or in early stages of planning (BlueMUSE for ESO/VLT; Richard et al, 2019).…”